In situ formation of reactive barriers for pollution control

ABSTRACT

A method of treating soil contamination by forming one or more zones of oxidized material in the path of percolating groundwater is disclosed. The zone or barrier region is formed by delivering an oxidizing agent into the ground for reaction with an existing soil component. The oxidizing agent modifies the existing soil component creating the oxidized zone. Subsequently when soil contaminates migrate into the zone, the oxidized material is available to react with the contaminates and degrade them into benign products. The existing soil component can be an oxidizable mineral such as manganese, and the oxidizing agent can be ozone gas or hydrogen peroxide. Soil contaminates can be volatile organic compounds. Oxidized barriers can be used single or in combination with other barriers.

[0001] This application is a continuation in part of U.S. applicationSer. No. 09/429,878 filed Oct. 29, 1999, the disclosure of which ishereby incorporated by reference, and which is a continuation in part ofU.S. application Ser. No. 09/429,235 filed Oct. 28, 1999, now abandoned.

[0002] This invention was made with Government support under ContractNumber DEAC0676RLO1830 awarded by the U.S Department of Energy. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

[0003] The invention relates to methods and apparatuses for deliveringreagents and forming reactive barriers for pollution control.

BACKGROUND OF THE INVENTION

[0004] One persistent global challenge is the management and remediationof pollution. Pollution can take several forms, one of which includesland or soil pollution. Soil at a variety of depths beneath the ground'ssurface can become contaminated with pollutants from a wide variety ofsources. Soil pollution includes contamination of soil in the Vadosezone, meaning soil that is not saturated with water between the groundsurface and a point below the ground surface where the soil becomessaturated with water. Soil pollution can also occur in groundwater,meaning any regions of the soil below the Vadose zone that are saturatedwith water.

[0005] Contamination from a point source in the Vadose zone can disburseoutward from the source. Contaminants can also disburse from the Vadosezone into underlying groundwater. Groundwater typically has a gradientor flow pattern, wherein groundwater flows through the saturated soilmatrix while solid soil particles remain in place. Accordingly, whencontaminants reach groundwater, the contaminants can potentially spreadwith the groundwater more rapidly than they would otherwise fromdispersion in the Vadose zone.

[0006] The problem of contaminants spreading by dispersion in the Vadosezone, groundwater flow, or other mechanisms is widely recognized.Accordingly, a wide variety of methods and apparatuses have beendeveloped to counteract contamination of increasingly large areas ofsoil caused by contaminants spreading.

[0007] One such technology provides the creation of reactive barriers insoil that can be contacted with contaminated groundwater or dispersionfrom contaminated Vadose zone soil. A reactive barrier can beestablished by digging a trench into which a reactive substance can beplaced and then backfilling the trench. One such reactive substanceincludes zero-valent iron in the form of iron filings that acts as areducing agent on a variety of contaminants. Groundwater containingtargeted contaminants can flow through the iron filings deposited in atrench and flow out of such iron filings as treated ground water.

[0008] While some success has been achieved in establishing reactivebarriers in trenches, the life of such a barrier is finite. Depending ona variety of conditions, including the level of contamination, thereagents in the barrier will ultimately be consumed. Once the reactionwith contaminants ceases, additional reactive materials must again beplaced in a trench and backfilled to continue the treatment ofgroundwater in situ.

[0009] It would be very unusual for a reactive barrier, as describedabove, to maintain its reactivity long enough to effectuate completetreatment of groundwater contaminates. Rather, the most commoncircumstance is that protection against spreading of contaminates willendure for a time and then cease. Thus, a need exists for reactivebarriers that will persist long enough to prevent contaminant spreadingas long as the contamination exists. Improved techniques are also neededfor efficiently constructing reactive barriers and for creating moreeffective barriers that minimize the disruption to the existing soil.Such reactive barriers are needed to alleviate the spreading ofgroundwater contamination as well as Vadose zone contamination. Withoutsuch advances, the current challenges of isolating and remediating soilcontamination will continue to exist.

SUMMARY OF THE INVENTION

[0010] In accordance with one aspect of the invention, soilcontamination is treated by forming a barrier of oxidized soil material.The oxidized barrier is formed by delivering an oxidizing agent into theground to oxidize an existing soil component, and the barrier is formedin the path of contaminate migration to neutralize percolating soilcontamination. The oxidized material reacts with soil contaminatemigrating into the barrier to reduce the level of the soil contaminatemigrating through the barrier to acceptable levels. The existing soilcomponent can be a naturally occurring mineral, such as manganese, andthe oxidizing agent can be ozone.

[0011] In accordance with another aspect of the invention, a reagentdelivery method includes positioning reagent delivery tubes in contactwith soil. The tubes can include a wall that is permeable to asoil-modifying reagent. The method further includes supplying thereagent in the tubes, diffusing the reagent through the permeable walland into the soil, and chemically modifying a selected component of thesoil using the reagent. The tubes can be in subsurface contact withsoil, including groundwater, and can be placed with directional drillingequipment independent of groundwater well casings. The soil-modifyingreagent includes a variety of gases, liquids, colloids, and adsorbentsthat may be reactive or non-reactive with soil components. In accordancewith various aspects of the invention, the method may be used to formreactive barriers, control pests, enhance soil nutrients for microbesand plants, and serve other functions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0013] FIGS. 1-6 are perspective views of various isometric soilportions.

[0014] FIGS. 7-9 are side views of exemplary reagent distributionmatrices.

[0015]FIG. 10 is a top schematic view of a well system useful increating an oxidized barrier.

[0016]FIG. 11 is a side sectional view illustrating delivery of areactive gas to saturated soil portions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0018]FIG. 1 illustrates a soil portion 10 including a Vadose zone 10 aand an area of water-saturated soil (i.e., groundwater) 10 b. In thecontext of this document, the terms “soil” and “soil portion” compriseall matter at and below the ground surface, regardless of its locationor composition. For example, matter at and below the floor of a body ofwater is within the meaning of “soil.” Accordingly marine sediment isconsidered soil. Also accordingly, “soil” and “soil portion” include allof the solid, liquid, and/or gaseous components of such soil.

[0019] Vadose zone 10 a extends from a ground surface 11 downward to thepoint where soil becomes saturated with water and groundwater 10 bbegins. Multiple regions of water-saturated soil can exist below Vadosezone 10 a forming a variety of groundwater regions or aquifers. FIGS. 1and 2 have been drawn simplified form for the sake of explanation but donot limit the present invention to application in only one groundwaterregion, aquifer, or other soil portion saturated with water. FIG. 1 alsoillustrates a direction of flow for a contaminated groundwater flow 12 ain groundwater 10 b. The infiltration of a surface water flow 14 isindicated downwardly from ground surface 11 into Vadose zone 10 a andtoward groundwater 10 b. Sources of surface water flow 14 include, forexample, rainfall and above-ground bodies of water. An area of amodified soil 16 is formed in soil portion 10. A contaminant source 18is also illustrated along with a boundary line for a disbursedcontaminant 19. FIG. 2, illustrating soil portion 20, includes all theelements of soil portion 10 illustrated in FIG. 1, except that an areaof a modified soil 26 is provided in the alternative to modified soil16.

[0020] One difference between modified soil 16 and modified soil 26 istheir respective orientation. Modified soil 16 is shown orientedapproximately vertically and extending from ground surface 11 throughVadose zone 10 a and into groundwater 10 b. Depending on the intendedfunction for modified soil 16, such modified soil may or may not extendfully through soil portion 10 as shown in FIG. 1. Rather, it isconceivable that modified soil 16 can only exist within Vadose zone 10a, within groundwater 10 b, or in some other configuration. Similarly,modified soil 26 can exist at any depth below ground surface 11,including zero depth, or at ground surface 11. It is further conceivablethat modified soil 16 can be oriented in some fashion other thanindicated in FIG. 1, approximately vertically, or in FIG. 2,approximately horizontally. For selected purposes, some of which aredescribed herein, certain advantages may exist to orienting modifiedsoil 16 approximately vertically and modified soil 26 approximatelyhorizontally

[0021] One aspect of the present invention provides a method for reagentdelivery that includes positioning one or more reagent delivery tubes incontact with the soil. If desired, the reagent delivery tubes can be insubsurface contact with the soil. At least a portion of at least one ofthe tubes can comprise a wall that is permeable to a soil-modifyingreagent. The reagent can be supplied into the tube, diffusing thereagent through the permeable wall and into the soil. Once in the soil,the reagent can be used to chemically modify a selected component of thesoil. Soil components can include any solid, liquid, and/or gas, inparticular, groundwater and components within its liquid phase. Notably,the reagent delivery tubes can be positioned in a variety ofconfigurations to accomplish the above-described aspect of the presentinvention, as well as other aspects. Accordingly, the above-describedreagent delivery method can be used to establish an area of modifiedsoil, such as modified soil 16 or modified soil 26. The approximatelyvertical orientation of modified soil 16, the approximately horizontalorientation of modified soil 26, or some other orientation can beestablished by the positioning of the reagent delivery tubes.

[0022] There exists at least three mechanisms envisioned by the presentinvention in which soil or its properties can be modified. First, areagent can react directly with a contaminant or other solid component.Second, a secondary reaction of a reagent with a contaminant can occur,such as when oxygen enhances already existing microbial reactions.Third, modification of soil components or soil properties can causeexisting soil components to react with contaminants. Such is the casewhen hydrogen sulfide reduces existing iron oxide in soil, thus allowingreduced iron to react with contaminants or other components. Sodiumdithionite can also be used to reduce naturally occurring iron in soil.Iron can also be introduced into soil as a colloid. Other reducingagents include ammonium oxalate. Examples of adsorbents includequaternary ammonium amine compounds and surface-modified clay colloids.

[0023] In another aspect of the invention, an oxidizing agent is used toform a reactive barrier by modifying the soil according to this thirdmechanism. An oxidizing agent can be introduced to react with existingsoil components to create an oxidized reactive barrier that in turnreacts with contaminants. For example, ozone can be used to oxidizenaturally occurring minerals in the soil. The oxidized form of themineral can then react with constituents such as metals, organics, andradionuclides associated with or moving through the oxidized zone undernatural gradients.

[0024]FIG. 3 illustrates a soil portion 30 including reagent deliverytubes 37 in subsurface contact with a soil as indicated by theirposition below ground surface 11. A reagent is supplied in tubes 37 anddiffused through the permeable walls and into soil portion 30 asindicated by a boundary surrounding each tube 37 indicating the extentof a modified soil 36. In FIG. 3, the areas of modified soil 36surrounding tubes 37 are shown to overlap. Tubes 37 are positionedsubstantially parallel to one another and a majority of tubes 37 areapproximately coplanar. More specifically, each of tubes 37 lie in thesame approximately vertical plane and, thus, all of tubes 37 arecoplanar. Accordingly, the overlapping areas of modified soil 36 form asubstantially vertical overall area of modified soil analogous tomodified soil 16 shown in FIG. 1. It is conceivable that tubes 37 couldalso be positioned substantially parallel to one another, but with lessthan a majority of tubes 37 being substantially coplanar. Depending onthe particular arrangement, an overall area of modified soil analogousto modified soil 16 shown in FIG. 1 could nevertheless be formed.

[0025] It should be noted that soil portion 30 of FIG. 3 is presented ina more simplified form compared to soil portions 10 and 20 in FIGS. 1and 2. Even though no distinction is made in soil portion 30 as to aVadose zone or groundwater, modified soil 36 can exist in any Vadosezone, groundwater, and/or other region of a soil portion presentedherein or otherwise in existence.

[0026] Further note should be made that each of tubes 37 possesses alongitudinal axis that is oriented within about 45° of horizontal. Morespecifically, assuming ground surface 11 is approximately horizontal,each of tubes 37 is also approximately horizontal. The advantages to beobtained by orienting reagent delivery tubes with about 45° ofhorizontal are surprising. One such advantage is that such positioningallows the use of directional drilling equipment to emplace tubes 37.Directional drilling equipment is currently being used in the placementof electrical and other underground transmission cables. The technologyallows placement of such cables at varying depths and horizontal runs ofvarying lengths. If a horizontal run is not desired, then the technologywill allow an angled run, for example within about 45° of horizontal.

[0027] Placing tubes 37 approximately horizontal can provide severaladvantages. One advantage is that delivery of reagent to a large regionin the path of moving groundwater can be accomplished with minimaldisturbance of the ground surface. From a starting location, a tube 37can be extended to a distance as great as the directional drillingequipment will reach. Subsequent tubes 37 may be placed at other depths,perhaps from the same starting location, to established a desiredarrangement of tubes 37. If conventional vertical well casings wereinstead used for reagent delivery, then conventional drilling equipmentwould set up and drill every several feet for each well casing. Thus,tubes 37 can be placed to intercept groundwater with a minimum of accessholes relative to conventional techniques. Further, tubes 37 could beplaced to maximize contact with a selected geologic strata that maypreferentially contain contaminants.

[0028] Tubes 37 may also be placed substantially parallel andsubstantially coplanar with directional drilling equipment. Givenpotential variations in precise placement of tubes 37, some misalignmentfrom exactly parallel or an exact plane may occur, but can be acceptablein many cases. Areas of modified soil 36 can be designed to overlap suchthat substantially parallel and substantially coplanar tubes 37nevertheless provide a desired effect.

[0029] Another advantage of the various aspects of the present inventionis that minimal energy is required to operate the technology. A reagentflow can be provided to the apparatus using a gravity-fed tank orcontainer. Alternatively, a pump can be utilized to supply theapparatus. Gaseous reagents can similarly be provided from apressure-regulated vessel. As a result of such features, the presentinvention can be considered to provide a semi-passive reactive barrier.Such is opposed to a passive reactive barrier, one example of which hissolid iron filings placed in a trench and backfilled.

[0030] Still another advantage of the various aspects of the inventionis that enhanced delivery of reagents to surrounding soil can beachieved. Reagents may be supplied to modify soil in bulk form, that is,for gases, as gas bubbles, and for liquids, as droplets or stream flow.Particularly in the case of gases, bubbles do not diffuse reagents intosoil in an efficient manner. By comparison, molecular diffusion ofreagents through a permeable wall and into surrounding soil provides thereagents in a form that will readily modify selected soil properties orcomponents. If bubbles are instead provided, then the reagents in thegas bubbles can diffuse from bubbles into the same molecular formprovided from a reagent delivery tube with a permeable wall.Accordingly, improved modification and dispersion of reagents deliveredthrough a tube can be provided in the various aspects of the presentinvention.

[0031] A variety of materials may be used to enable molecular diffusionthrough a permeable wall of a reagent delivery tube. Generally, suchmaterials are preferably substantially amorphous. A highly cross-linkedpolymer material may hinder diffusion, but a less cross-linked materialcan allow more diffusion. A material that is completely amorphous, withno particular ordered arrangement of molecules and/or atoms, will oftenallow the most diffusion. The desired degree to which the materialcomprising a permeable wall is amorphous may depend on the particularreagents to be diffused and the desired diffusion rate. A few examplesof suitable materials include silicone tubing, neoprene tubing(synthetic rubber available from Norton Performance Plastics in Wayne,N.J.), and TYGON™ tubing (silicone tubing also available from NortonPerformance Plastics). Natural rubber, gum rubber, substantiallyamorphous polyurethane, and substantially amorphous polyethylene mayalso be suitable.

[0032] Conventionally, subsurface reagent delivery equipment hasutilized installation of a perforated or otherwise porous well casing.Once installed, reagents can be directly injected into the conventionalwell casing and thereafter diffuse into surrounding soil. By comparisonto the various aspects of the present invention, subsurface reagentdelivery through a perforated well casing is rather limited andineffective. Placing perforated well casings in the positions shown fortubes 37 in FIG. 3 would require excavation and backfilling. Yet,directional drilling equipment can quite easily place tubes 37 parallelto one another in a vertical plane, wherein tubes 37 are placed atvarying depths below ground surface 11. Further, placing reagentdelivery tubes in contact with soil provides release of reagent directlyto an affected area.

[0033] Other methods for placing tubes 37 in the described positions arealso available. For example, one tube 37 can be placed in the bottom ofa trench which is then backfilled to the point where a second tube 37 isto be placed. Successive backfilling and placement of additional tubes37 will result in the orientation illustrated in FIGS. 3. In moredetail, such a method includes exposing subsurface soil, placing one ormore of tubes 37 in contact with the subsurface soil, and backfillingthe exposed subsurface soil.

[0034]FIG. 4 illustrates soil portion 40 wherein reagent delivery tubes47 are positioned in subsurface contact with soil portion 40 belowground surface 11. By supplying a reagent in tubes 47, an area ofmodified soil 46 can be established surrounding each tube 47. In FIG. 4,the longitudinal axis of each tube is oriented approximatelyhorizontally, tubes 47 are approximately parallel, and each tube 47 isapproximately coplanar. However, in contrast to tubes 37 in FIG. 3,tubes 47 in FIG. 4 are positioned in an approximately horizontal plane.Accordingly, the overlapping areas of modified soil 46 form an overallarea of modified soil similar to modified soil 26 illustrated in FIG. 2.The positions shown in FIG. 4 are also conducive to placement either bydirectional drilling equipment or by exposing subsurface soil andbackfilling after placing tubes in contact with the subsurface soil. Asan alternative to FIG. 4, tubes 47 could be arranged radially, extendingoutward from a common area of origin. Tubes 47 could still be positionedin an approximately horizontal plane, but they would not be parallel.

[0035]FIG. 5 illustrates soil portion 50 with tubes 57 positioned withtheir longitudinal axes approximately vertical. Even though tubes 57 arenot within about 45° of horizontal, tubes 57 are approximately paralleland approximately coplanar. Thus, the overlapping areas of modified soil56 form an overall area of modified soil similar to modified soil 16illustrated in FIG. 1. Tubes 57 can be placed using directional drillingequipment or by exposing subsurface soil and backfilling after placingtubes 57 in contact with the subsurface soil. As an alternative to FIG.5, tubes 57 could be arranged radially, extending downward from a commonarea of origin. Tubes 57 could still be positioned in an approximatelyvertical plane, but they would not be parallel.

[0036] In FIG. 6, soil portion 60 includes ground surface 11 below whichtube 67 is placed in subsurface contact with soil. Tube 67 includes aplurality of parallel tubular sections that are approximately linear.Linear sections 67 a are shown with their longitudinal axis orientedapproximately horizontally. Alternatively, although now shown, thelongitudinal axes of linear sections 67 a could be orientedapproximately vertically or at some other position. Tube 67 furtherincludes one or more curved sections 67 b joined to linear sections 67 ato form a serpentine pattern.

[0037] Although linear sections 67 a of tube 67 are approximatelyparallel and approximately coplanar in the shown configuration, otherconfigurations are, of course, possible. A plane defining the relativeposition of linear sections 67 a is approximately vertical in the shownconfiguration. Tube 67 thus produces an area of modified soil 66 that isapproximately vertical, resembling modified soil 16 of FIG. 1.Alternatively, tube 67 can be oriented as shown but with the planedefining the position of linear sections 67 a oriented approximatelyhorizontally. In such a configuration, an area of modified soil would beproduced resembling modified soil 26 of FIG. 2.

[0038] The various tubes of FIGS. 3, 4, and 6 individually comprise amajor portion sized and oriented to provide an individual verticaldistance of reagent distribution in the soil and an individualhorizontal distance of reagent distribution in the soil greater than thevertical distance. In FIG. 5, unless the length of tubes 57 is unusuallyshallow, the horizontal distance of reagent distribution is less thanthe vertical distance. If the length of tubes 57 is less than thehorizontal distance of reagent distribution indicated by the area ofmodified soil 56, then the horizontal distance of reagent distributioncould be greater than the vertical distance for tubes 57.

[0039]FIG. 6 further illustrates tube 67 including one or more curvedsections and a plurality of approximately linear sections, wherein themajor portion of each tube comprises one of the linear sections. Also inFIGS. 3, 4, and 6, a longitudinal axis of the major portion of one ormore individual tubes is oriented within about 45° of horizontal. Asdescribed, individual tubes are more specifically oriented approximatelyhorizontally.

[0040] The various tubes of FIGS. 3-6 can be in subsurface contact withboth soil and groundwater. Further, selected portions of the tubes maybe permeable to a soil-modifying reagent while other portions are notpermeable. Thus, selected portions of soil can receive the reagentdiffusing through the permeable wall while other portions do not. Such aconfiguration would allow a tube to extend from ground surface 11through Vadose zone 10 a and into groundwater 10 b without releasing anyreagent into Vadose zone 10 a, but instead affecting groundwater 10 b ora portion thereof.

[0041] The materials and constructions of the tubes can vary dependingon the reagent to be dispersed with the tubes. In one aspect of theinvention, the permeable wall of a reagent delivery tube can comprise ashell having openings therein and a reagent permeable liner in contactwith an inner surface of the shell. By this means, a thin permeableliner can be provided with structural integrity sufficient so that itcan be placed in subsurface contact with soil. It may further bedesirable that the opening in the shell forming the permeable wallcomprise pores that are intrinsic to a material comprising the shell.Pores intrinsic to a material can be distinguished from orificesmechanically formed in a shell. Of course, tubes can be used having apermeability intrinsic to the material comprising a shell such that nopermeable liner is required.

[0042] The permeability of the permeable wall of a tube depends upon theparticular reagent to be delivered. The particular reagent depends uponthe objective of modifying the soil. One advantage of the presentinvention is that it chemically modifies a selected component of thesoil using the reagent. The soil modifying reagent can comprise a gas, aliquid, a colloid, or yet other materials, but preferably a gas. Any ofsuch reagents may further be described as a reducing agent, an oxidizingagent, a microbe, an enzyme, or an adsorbent. Each of such reagents maychemically modify a selected component in the soil. The soil may bechemically modified by treating a contaminant found therein.Alternatively, a reagent may produce a chemically modified component ofthe soil that in turn reacts with a soil contaminant, even though thereagent does not directly react with a soil contaminant. Examples of afew soil contaminants include a metallic ion, a hydrocarbon, or ahalogenated hydrocarbon.

[0043] Another advantage of the present invention is that it can modifya selected property or component of at least one of the soil andgroundwater using a gaseous reagent. In such case, a gas permeable tubewall is preferred. Possible soil modifying reagents to accomplish suchan advantage include a reducing agent, an oxidizing agent, an oxygensource, an oxygen displacer or scavenger, a microbial nutrient, aco-metabolite, a pesticide, a fertilizer, or a herbicide, each of whichmay be provided in a gaseous form.

[0044] Some of such reagents are not reactive with soil components,while others can be selected to react with a soil contaminant. Gaseousreducing agents and oxidizing agents may chemically modify components ofthe soil, including contaminants. An oxygen source can be used toenhance a microbial reaction occurring in the soil, wherein themicrobial reaction chemically modifies a selected component of the soil.Thus, supplying an oxygen source modifies the property of oxygen contentin soil, rather than modifying a particular component of soil. Providingan oxygen displacer or scavenger is analogous except that an anoxiccondition can be created. Generally, an anoxic condition might bedesired for other microbial reactions. A microbial nutrient can providea similar enhancement. A pesticide may also be supplied to provide theadvantage of pest control in a selected soil portion. Fertilizer may beprovided to enhance plant growth in a selected soil portion. A herbicidemay be provided to suppress plant growth in a selected soil portion.

[0045] Another aspect of the invention comprises a reactive reagentreacting with a selected component of the soil. Accordingly, creating anarea of modified soil as depicted in FIGS. 1-6 can create a rechargeablereactive barrier. That is, a reactive reagent may be supplied fromreagent delivery tubes to a selected soil portion where the reagent willreact with existing selected components in such soil portion. Asillustrated in FIG. 1, contaminated groundwater 12 a flows throughmodified soil 16. Assuming modified soil 16 is a rechargeable reactivebarrier, contaminants or other soil components moving with contaminatedgroundwater flow 12 a will pass through the rechargeable reactivebarrier for treatment. Treated groundwater flow 12 b then flows out fromthe rechargeable reactive barrier. A continuous supply of reactivereagent into modified soil 16 will match the continuous supply of soilcontaminants or other components flowing with groundwater 10 b.

[0046] Referring to FIG. 2, assuming modified soil 26 is a rechargeablereactive barrier, any contaminant or other soil component infiltratingwith contaminated surface water flow 14 a will pass through therechargeable reactive barrier. Treated surface water flow 14 b thenenters groundwater 10 b. One potential use for such a method is inpreventing contamination of groundwater with organic and inorganicbyproducts of a cattle feed lot, including viruses. Other analogous usesare also conceivable. Examples of reactive reagents, which happen to begaseous reactive reagents, include chlorine, sulphur dioxide, bromine,acetylene, ozone, hydrogen sulfide, or combinations thereof. Some ofsuch reagents can provide reaction with a selected component in the soiland subsequent reaction of the selected component with a soilcontaminant. Of course, a gaseous, reactive reagent can also reactdirectly with a contaminant.

[0047] Where the reagent is ozone, the ozone can react with an existingmineral in the soil to create an oxidized zone or barrier. Such anoxidized barrier can react with soil contaminates percolating throughthe zone to degrade the contaminates into benign species. In oneexample, existing manganese in the soil can be oxidized to permanganateby ozone. The formed permanganate can then react with soil contaminates,such as TCE and DCE, to form degraded contaminates and benign products.

[0048] A rechargeable, reactive barrier may similarly be establishedthrough a microbial reaction. Such microbial reactions can be enhancedby providing an oxygen source or an oxygen displacer or scavenger asrequired by the particular type of reaction. A microbial nutrient or aco-metabolite are other reagents that may be supplied according to thepresent invention to enhance the microbial reaction.

[0049] In another aspect of the invention, pest control can be providedby positioning one or more reagent delivery tubes in contact with asoil. At least a portion of at least one of the tubes can comprise awall that is permeable to a pest control reagent. The pest controlreagent can be supplied in the tube and diffused in an effective amountthrough the permeable wall and into the soil. If desired, the reagentdelivery tubes can be in subsurface contact with the soil. One potentialagricultural aspect includes placing reagent delivery tubes in furrowsof an agricultural field and supply pesticide. An example of a pest is aroot nematode. Such a method can enhance the safety of using somepesticides, such a methyl bromide, and also reduce the amount requiredby localizing application in the area most needed.

[0050] Another use of pesticide reagent delivery tubes involvesprotecting subsurface structures from pest damage or infestation.Examples of pests include termites and ants. Tubes may be positioned aneffective distance from a subsurface structure to effectuate a pestcontrol in soil juxtaposed with the structure. Such may be accomplishedwith directional drilling equipment, the trench and backfill methoddescribed above, or perhaps other methods. In a similar manner, plantcontrol can be provided by positioning one or more herbicide reagentdelivery tubes in contact with a soil. Such may be useful in suppressingplant growth in designated areas and suppressing root damage ofsubsurface structures.

[0051] FIGS. 7-9 illustrate further aspects of the present inventionwith their depiction of a few examples of alternative embodiments to thereagent delivery tubes illustrated in FIGS. 3-6. One difference betweenthe tubing of FIGS. 3-6 and the tubing of FIGS. 7-9, is that the latterare linked together such that a preselected spacing between tubingsections is provided and maintained when the apparatuses are positionedin or on soil. Because of the linked feature, the apparatuses of FIGS.7-9 will generally be installed in trenches or other excavations thatare then backfilled. Notably, such trenches or other excavationsexposing the subsurface soil may be constructed in a manner that allowsthe apparatuses of FIGS. 7-9 to be positioned in an approximatelyvertical plane, an approximately horizontal plane, or even some otherplane. Further, assuming that the apparatuses of FIGS. 7-9 are at leastsomewhat flexible, the apparatuses could be oriented such that tubesections are not necessarily coplanar. For example, such apparatusescould be placed in a curved trench or some other nonplanar trench orexcavation.

[0052] Nevertheless, because the apparatuses of FIGS. 7-9 includereagent delivery tube sections, they may be used in the methodsdescribed above to form modified soil portions, such as modified soil16, modified soil 26, or yet other areas of modified soil. It is notpresently anticipated that the apparatuses of FIGS. 7-9 can be installedusing directional drilling equipment. Nevertheless, it is conceivablethat currently existing or later developed equipment could potentiallybe used to position the apparatuses of FIGS. 7-9. A method may be usedother than one requiring exposure of subsurface soil, placement of theapparatuses, and backfilling the exposed subsurface soil.

[0053] In FIG. 7, a magnified view of a geotextile fabric forming amatrix 70 is illustrated. A reagent flow 72 can be introduced intohollow tubular sections 74, hollow tubular sections 76, or both. Matrix70 of FIG. 7 can be a woven fabric, wherein tubular sections 74 andtubular sections 76 intersect at cross-overs 78. Since tubular sections74 and tubular sections 76 intersect at cross-overs 78, they canadditionally be linked in some fashion at cross-overs 78. If matrix 70is woven then tubular sections 74 and 76 will likely remain in theirrespective positions without some sort of line at cross-overs 78.However, if matrix 70 is not woven or if the gaps between approximatelyparallel tubular sections are large enough to allow shifting, then suchlinking may be desired.

[0054] It is further noted that only a portion of tubular sections 74 or76 may comprise reagent delivery tubes and yet matrix 70 may stillaccomplish soil modification as described above. A variety ofconfigurations are conceivable. For example, only tubular sections 74,as shown in FIG. 7, may be used to deliver reagent, while tubularsections 76 simply provide a woven, fabric-like feature or some otherspacer-type of feature. Accordingly, tubular sections 76 may besubstituted for other structures that are not tubular and might notfunction as reagent delivery tubes. Further, for example, only aselected portion of tubular sections 74 might be used for reagentdelivery. Because the boundary of modified soil can extend beyond thediameter of an individual tubular section 74, the reagent delivery tubesin matrix 70 need not be directly adjacent to one another. Some numberof tubular sections 74 or thoer non-tubular structures can exist betweenthe tubular sections 74 used for reagent delivery. Even so, theoverlapping boundaries of modified soil around individual reagentdelivery tubes can still provide an area of modified soil such asmodified soil 16, modified soil 26, or some alternative.

[0055] In FIG. 8, a matrix 80 is illustrated wherein reagent flow 72 issupplied through tubular sections 84 and tubular sections 86. Tubularsections 84 and 86 intersect to form reagent distribution junctions 88.Because tubular sections 84 and 86 are linked by distribution junctions88, reagent flow 72 supplied at a single tubular section, or a fewtubular sections, will quickly spread throughout matrix 80. The spacingbetween parallel tubular sections 84 and parallel tubular sections 86may be greater than the distance between parallel tubular sections 74and 76 illustrated in FIG. 7. A greater distance may be warranted giventhe potentially increased cost of fabricating matrix 80 withdistribution junctions 88, as compared to a woven fabric of matrix 70with cross-overs 78. FIG. 8 illustrates matrix 80 as having distributionjunctions 88 at each intersection of tubular sections 84 and 86.Nevertheless, it is conceivable that distribution junctions 88 may onlybe provided at a portion of the intersections.

[0056] In FIG. 9, a matrix 90 is illustrated wherein reagent flow 72 issupplied into a tubular section 94 which distributes reagent flow 72 tomultiple tubular sections 96. Tubular sections 96 are further providedwith one or more spacers 99 to maintain tubular sections 96 in anapproximately parallel configuration. Thus, FIG. 9 represents simply oneadditional variation on the reagent delivery apparatuses described inFIGS. 7 and 8. Other variations are, of course, encompassed by thepresent invention.

[0057] Depending on the placement and configuration of the apparatusesof FIGS. 7-9, such apparatuses can accomplish reagent delivery whereinone or more reagent delivery tubes are in contact with a soil. At leasta portion of at least one of the tubes can include a wall that ispermeable to a reagent. If desired, the reagent delivery tubes can be insubsurface contact with the soil. Preferably, the tubes can individuallycomprise a major portion sized and oriented to provide an individualvertical distance of reagent distribution in the soil and an individualhorizontal distance of reagent distribution in the soil greater than thevertical distance. As illustrated in FIGS. 7-9, a reagent deliveryapparatus may also be provided comprising a reagent distribution matrix.At least a portion of the matrix can include a plurality of paralleltubular sections and a wall permeable to the reagent, the wall being incontact with a soil, perhaps in subsurface contact.

[0058] Each of FIGS. 7-9 further illustrates how such an apparatus cancomprise one or more spacers extending between adjacent tubularsections. Such structures can comprise a dual function of both a spacerand a tubular section. The longitudinal axis of at least a portion ofthe tubular sections in the apparatuses in FIGS. 7-9 can be orientedwithin about 45° of horizontal. Thus, the unique tubing orientation ofFIGS. 3 and 4 can be provided by the apparatuses of FIGS. 7-9.

[0059] In yet another aspect of the present invention, a reagentdelivery apparatus can comprise a reagent distribution matrix, whereinat least a portion of the matrix comprises a wall permeable to reagent,a first plurality of parallel tubular sections, and a second pluralityof parallel tubular sections. If desired, the reagent delivery tubes canbe in subsurface contact with the soil. The longitudinal axis of atleast a portion of the first tubular sections can be substantiallyperpendicular to a longitudinal axis of at least a portion of the secondtubular sections. FIGS. 7 and 8 each illustrate such an apparatus.

[0060] In yet another aspect of the invention, soil contamination istreated by forming one or more zones of oxidized material in the path ofpercolating groundwater, such as modified soil portions 16 of FIG. 1.The zone is formed by delivering an oxidizing agent into the ground forreaction with an existing soil component. The oxidizing agent modifiesthe existing soil component creating the oxidized zone. Subsequentlywhen soil contaminates migrate into the zone, the oxidized material isavailable to react with the contaminates and degrade them into benignproducts.

[0061] The existing soil component can be any oxidizable soil componentthat, at least in oxidized form, is capable of contributing to thedegradation of a soil contaminate. In one aspect the existing soilcomponent is a naturally occurring oxidizable inorganic material such asa mineral. Once formed, the oxidized form of the soil component can thenreact with other soil constituents such as metals, organics, andradionuclides associated with or moving through the oxidized zone undernatural gradients.

[0062] Abundant oxidizable soil components include the metals manganeseand iron and some of their oxide forms (i.e., manganese dioxide andferrous oxides). As an example, manganese can be oxidized topermanganate, a substance that is known to degrade volatile organiccompounds, such as TCE and DCE. It is believed that the degradationpathway for TCE reacting with permanganate proceeds through theformation of an intermediate cyclic complex with subsequent breakdown tobenign substance (e.g. carboxylic, carbon dioxide, chloride ions) andmanganese dioxide. Permanganate may be regenerated by the reoxidation ofmanganese dioxide. Similar processes also occur for metallic iron andits oxide forms.

[0063] Manganese useful in practicing the present invention is presentin small amounts in most crystalline rocks. As a weathering product ofcrystalline rocks it may be redeposited as various minerals, but chieflyas pyrolusite. Manganese containing minerals are also found inlimestones and clays. Examples of other minerals containing manganeseinclude tourmaline, axinite, pryolusite, psilomelane, wolframite,manganite, columbite-tantalite, franklinite, rhodonite, rhodocrosite,the amphilboe group of minerals, johannsenite and augite.

[0064] The existing geologic material, such as manganese, can beoxidized by reaction with any oxidant of sufficient strength to oxidizeat least a portion of the existing geologic material. In oneadvantageous aspect of the invention, the oxidant reacts with theexisting soil material in a reaction that results in a minimum of toxicbyproducts. In one particular aspect the oxidant is ozone. It isbelieved that the oxidation of manganese to permanganate using ozoneproduces essentially no toxic byproducts, as the decomposition productof ozone is oxygen. Alternatively, the oxidant could be hydrogenperoxide, which likewise decomposes into harmless byproducts.

[0065] The oxidant can be delivered to the soil by any known method,including for example any of the delivery methods disclosed above. Forinstance when the oxidant is gaseous ozone, delivery of ozone to thesoil can be accomplished by the apparatus and procedures described inU.S. Pat. No. 5,205,927 to Wickramanayake titled “Apparatus forTreatment of Soils Contaminated with Organic Pollutants,” which ishereby incorporated by reference.

[0066] In another aspect, an oxidant is delivered to the soil through asystem of injection and extraction wells. Turning now to FIG. 10, a topview of an oxidant injection system 105 as installed in the ground isshown. Center injection well 110 is surrounded by a number of extractionwells 120. The oxidizing reactant is injected into the subsurfacethrough the center well 110, for example under positive pressure.Negative pressure is then applied at the extraction wells 120 to helpdraw the oxidant through the soil allowing the oxidant to react withsoil constituents as it is drawn from well 110 to well 120. Accordingly,the well system 105 as configured in FIG. 10 would produce a generallycircular barrier zone around well 120 and generally within the circlecreated by wells 120. It is understood that the relative depth of thebarrier zone can be controlled by the subsurface location andconfiguration of the individual wells. Other configurations of injectionand extraction wells can also be utilized as would occur to those ofskill in the art.

[0067] The injection system 105 including injection and extraction wellsis believed to be of particular applicability to situations where thesoil components to be oxidized are within the unsaturated soil portion.Moreover, where the oxidant is gaseous, the system 105 can serve tocreate a relatively large oxidized barrier zone in a relatively shortperiod due to the high rate of permeability of gas through soil.

[0068] In other aspects, a sparging well delivery system can beutilized. Turning now to FIG. 11, systems 130 and 140 are shown. System130 includes a vertical sparging well 133 that extends into thesubsurface and at least partially into a saturated groundwater. Bubblesof injected gaseous oxidant 135 exit the well 133 and react with thegroundwater forming a zone 137 of oxidized groundwater. System 140, likesystem 130 has a sparging well 143 that extends into the subsurface andat least partially into a saturated groundwater zone. However, well 143has a horizontal portion from which bubbles 145 exit to react with thegroundwater and form zone 147 of oxidized groundwater.

[0069] In forming and utilizing an oxidized reactive barrier accordingto aspects of the present invention, it is generally advantageous tofirst identify a site of soil contamination. The site should have atleast one contaminate that is susceptible to degradation to benignproducts by reaction with an oxidant. Then, one can identify a directionof likely contaminate migration or percolation, or equivalently, one canassume migration in all directions.

[0070] One next can select the soil site for barrier formation. Thebarrier site would likely have a contaminate level relatively lower thanthe soil contaminate site. The barrier site can also be located adistance away from and spaced apart from the contamination site, and thebarrier can be located in the determined path of contaminate migration.

[0071] Once the site is selected, one next can identify the soilcomponents to be oxidized to form the barrier. The relativeconcentration and abundance of the identified components can then bedetermined by any known method or by estimation. If the identifiedcomponent is not naturally present in sufficient quantity to form anadequate barrier, for instance if the native soil content of theidentified mineral is too low, an alternative component can beidentified or the soil can be supplemented or otherwise modified tocause an adequate supply of existing oxidizable component to be present.

[0072] After determining the amount or approximate amount of theselected oxidizable soil components existing in the soil, the oxidant isadded to oxidize the selected soil component. The oxidant is added untila substantial amount of the available selected component is oxidized.The amount should be sufficient to create an oxidized barrier such thatlevels of a contaminate percolating through the barrier is substantiallyreduced. For instance, the reduction can be at least about 20%, morepreferably 50% and most preferably at least about 75% degradation of thecontaminate percolating into the barrier.

[0073] On one aspect, the addition of oxidant ceases once a sufficientamount of oxidant has been added to the soil to create the barrier.After the barrier is formed, the barrier remains and is available toreduce the level of contaminates percolating through the barrier for atime after the addition of oxidant has ceased. This time is preferablyat least one day and more preferably on the order of several weeks andmost preferable as long as several months to a year. If convenient,equipment used to deliver the oxidant, such as ozone injectionequipment, may optionally be removed and deployed at another locationonce the barrier is formed.

[0074] In one useful application, a barrier is created where the amountof contaminate percolating through a particular zone of soil isrelatively low. In other applications, a barrier or series of barriersare created to contain and treat higher levels of contaminateconcentrations. It is understood that for a fixed amount of oxidizedmaterial, the life of the barrier, and consequently the need to refreshor recharge the barrier, would be shortened by exposure to higher levelsof contamination percolation. It is also believed that the passage oftime will contribute to barrier degradation. Accordingly, depending onthe application, additional oxidant can be periodically reinjected tooxidize the existing soil component, which may become reduced or spentover time.

[0075] It is understood that the addition of the oxidizing agent to thesoil to create the oxidized barrier can have advantageous soilremediation effects by virtue of at least three different mechanisms.First, if there is contaminate already present in the area, the oxidantcan react directly with the contaminant to produce a degradedcontaminant and benign products. Second, the oxidant can react with thenatural mineral to produce an oxidized species that in turn reacts witha contaminate to produce a degraded contaminate and a benign byproducts.Third, the oxidant can regenerate a reduced species that had previouslyreacted with a contaminate, for example iron (Fe2+), to allow theregenerated reduced species to again react with a contaminate.

[0076] It is also understood that the reactive barrier formed accordingto aspects of the present invention is formed in situ and utilizesexisting soil components as a substantial portion of the barrier.Accordingly, the overall hydrogology and permeability of the soil can berelatively unaffected because the barrier utilizes existing soilcomponents. Only an oxidant need be added to the soil to form thereactive barrier, though additional materials may optionally be added tomodify the soil in any desired manner.

[0077] By forming the barrier by the in situ oxidation of existing soilcomponents, the addition of potentially harmful materials to the soilcan be avoided. For example where existing manganese is oxidized withozone in situ, permanganate can be created in the soil where the onlybyproduct is oxygen. In this sense, the reactive barrier is formed in aprocess that is not disruptive to the existing soil composition.

[0078] This is to be contrasted with the direct addition of permanganateto the soil. In this latter procedure, permanganate is formed aboveground and provided to the soil as part of a compound. Aside from theproblems associated with creating and handling the permanganate andfinding a suitable injection medium, the injection of permanganate as acompound is a substantial modification of the soil and can lead toundesireable results. For example when injected as potassiumpermanganate, equal amounts of potassium are necessarily injected alongwith the permanganate, and high concentrations of potassium can beconsidered a soil contaminate, causing among other things waterdiscoloration.

[0079] In still other aspects of the invention, an oxidizing reactivebarrier can be used in combination with other reactive barriers, such asbarriers of reduced material. An example of a barrier of reducedmaterial are those constructed by reducing iron by injecting dithioniteas disclosed in U.S. Pat. No. 5,783,088 to Amonette et al. titled“Method of Removing Oxidized Contaminants from Water,” the disclosure ofwhich is hereby incorporated by reference. In one advantageous aspect, aseries of oxidizing and reducing barriers can be constructed in spacedapart alignment in the path of contamination percolation. For example aseries of concentric rings about a contaminate site or a series ofparallel walls in the path of groundwater percolation are two suchdesigns. By constructing a series of diverse barriers in this way, morevarious contaminates percolating in the groundwater can be degraded bysuch a multi-barrier system. Contaminates that are not degraded by onebarrier, for example the reduced barrier, can be degraded by the otherbarrier and vice versa.

[0080] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A method for treating soil pollution comprising: forming abarrier of oxidized soil material by delivering a gaseous oxidizingagent into the ground to oxidize an existing soil component, wherein thebarrier is formed in the path of contaminate migration; reacting theoxidized soil material with a quantity of soil contaminate migratinginto the barrier to reduce the level of the soil contaminate migratingthrough the barrier to an acceptable level.
 2. The method of claim 1wherein the oxidizing agent is ozone.
 3. The method of claim 1 whereinthe existing soil component is a mineral.
 4. The method of claim 3wherein the existing soil component is a naturally occurring mineral. 5.The method of claim 4 wherein the existing soil component is manganese.6. The method of claim 5 wherein the oxidizing agent is ozone.
 7. Themethod of claim 1 wherein the soil contaminate is a volatile organiccompound.
 8. The method of claim 7 wherein the oxidant is ozone.
 9. Themethod of claim 8 wherein the existing soil component is manganese. 10.The method of claim 1 wherein the reacting of the oxidized soil materialwith a quantity of soil contaminate occurs at least about 24 hours afterdelivery of the oxidizing agent ceases.
 11. A reactive barrier formationmethod comprising: identifying a quantity of minerals in the subsurface;delivering a quantity of an oxidizing agent into the subsurface tooxidize the identified minerals, wherein the quantity of deliveredoxidizing agent is sufficient to oxidize the identified minerals to forma reactive barrier of oxidized soil material, the reactive barriercomprising a sufficient quantity of oxidized soil material to reduce thelevel of a soil contaminate migrating through the barrier to anacceptable level.
 12. The method of claim 11 wherein the oxidizing agentis gaseous.
 13. The method of claim 12 wherein the quantity of mineralscomprise manganese.
 14. The method of claim 12 wherein the oxidizingagent is ozone.
 15. The method of claim 14 wherein the soil contaminateis a volatile organic compound.
 16. The method of claim 15 wherein thequantity of minerals comprise manganese.
 17. The method of claim 11wherein the oxidizing agent is selected from the group consisting ofhydrogen peroxide and ozone.
 18. A method for preventing the spread ofsoil pollution comprising: identifying a site of soil contaminationwherein the soil is contaminated by at least one soil contaminatesusceptible to degradation to benign products by reaction with anoxidant; determining a direction of contaminate migration; injecting anoxidizing agent into the ground in the path of the contaminatemigration; reacting the injected oxidizing agent with a naturallyoccurring soil component to form a treatment barrier of the oxidizednaturally occurring soil material; the treatment barrier being formed ofa sufficient quantity of oxidized soil material to reduce the quantityof the soil contaminate migrating through the barrier to an acceptablelevel before the soil contaminate leaves the barrier.
 19. The method ofclaim 18 further comprising reacting the oxidized soil material withcontaminate migrating into the treatment barrier.
 20. The method ofclaim 19 wherein the oxidizing agent is gaseous.
 21. The method of claim19 wherein the naturally occurring soil component comprise minerals. 22.The method of claim 21 wherein the minerals comprise manganese.
 23. Themethod of claim 22 wherein the oxidized naturally occurring soilmaterial comprises permanganate.
 24. The method of claim 22 wherein theoxidizing agent is ozone gas.
 25. The method of claim 21 wherein theoxidizing agent is selected from the group consisting of hydrogenperoxide and ozone.
 26. A reactive barrier formation method comprising:positioning one or more reagent delivery tubes in subsurface contactwith a soil; supplying an oxidizing reactive reagent to the soil throughthe tube; reacting the oxidizing reactive reagent with a naturallyoccurring component of the soil to form a reactive barrier; the reactivebarrier reacting with soil contaminates migrating into the barrier toreduce the level of soil contaminates migrating through the barrier toacceptable levels.
 27. The method of claim 25 wherein the oxidizingreactive reagent is ozone.
 28. The method of claim 26 wherein thenaturally occurring component of the soil comprises a soil mineral. 29.The method of claim 25 wherein the oxidizing reactive reagent isselected from the group consisting of hydrogen peroxide and ozone.
 30. Amethod for treating soil pollution comprising: forming a barrier ofoxidized soil material by delivering an oxidizing agent into the groundto oxidize an existing soil component, wherein the oxidizing agent isselected from the group consisting of ozone and hydrogen peroxide, andwherein the barrier is formed in the path of contaminate migration;reacting the oxidized soil material with a quantity of soil contaminatemigrating into the barrier to reduce the level of the soil contaminatemigrating through the barrier to an acceptable level.
 31. The method ofclaim 30 wherein the existing soil component is a mineral.
 32. Themethod of claim 31 wherein the existing soil component is a naturallyoccurring mineral.
 33. The method of claim 32 wherein the existing soilcomponent is selected from the group consisting of tourmaline, axinite,pryolusite, psilomelane, wolframite, manganite, columbite-tantalite,franklinite, rhodonite, rhodocrosite, the amphilboe group of minerals,johannsenite and augite.
 34. The method of claim 33 wherein the existingsoil component is pyrolusite.
 35. The method of claim 30 wherein thesoil contaminate is a volatile organic compound.
 36. The method of claim35 wherein the existing soil component is manganese.
 37. The method ofclaim 36 wherein the oxidant is ozone gas.